U.S. Pat. No. 5,765,839 describes a chuck having a chuck body rotatable about a chuck axis and provided centered on the axis with an annular array of teeth each having a steep flank and a shallow flank. A plurality of jaws angularly spaced on the body about the axis are radially displaceable relative to the body between inner and outer positions. A tightening ring is axially fixed but rotatable about the axis on the body in a tightening direction and in an opposite loosening direction. A pair of screwthread formations between the tightening ring and the jaws can move the jaws radially together on rotation of the tightening ring in the tightening direction and radially apart on rotation of the tightening ring in the loosening direction. A pawl engageable with the teeth and angularly fixed on the tightening ring can be radially displaced between a retaining position engaging the teeth and preventing rotation of the body relative to the tightening ring in the loosening direction and a freeing position permitting free rotation of the body relative to the tightening ring in both directions. A setting ring axially fixed but angularly displaceable on the tightening ring is formed with a pair of angularly spaced and radially open seats. A pair of angularly spaced abutments between the setting ring and the tightening ring limit angular movement of the sleeve on the ring to movement between a pair of end positions of the sleeve on the ring. A cam on the setting ring is engageable with the pawl for displacing the pawl into the retaining position when the setting ring is in one of its end positions and for displacing the pawl into the freeing position when the setting ring is in the other of its end positions. A latch member angularly fixed on the tightening ring is engageable in the seats of the setting ring for releasably retaining the setting ring in its end positions. A common spring extending angularly along and fixed angularly in the tightening ring urges the latch member into the seats and the pawl into the freeing position.
Thus with such a chuck, it is possible to hammer drill without the tightening ring reverse rotating to release the bit. In fact the chuck can be set up so that drilling creates a self-tightening action.
The main problem with this arrangement is that when the drill is subjected to considerable vibration or shocks directed radially of the chuck, the pawl can jump out of the teeth and allow the chuck to loosen. Today's chucks can operate at 6000 to 40,000 hammers per minute, so that they are subjected to enormous shock and stress. In addition, such a chuck is normally used under very difficult work conditions so such unintended loosening is a real problem.